Fifty-year dynamics in a temperate raptor assemblage

Abstract

Raptorial birds are popular monitoring objects worldwide; however, published data on long-term dynamics of raptor assemblages are scarce. This paper summarizes 50-year (1961-2010) raptor surveys in relation to landscape change in a 60 km 2 area near Saue, North Estonia. Altogether, 11 species of diurnal raptors and 7 species of owls were found nesting. Their total density stayed remarkably stable throughout the study period, but both annual species richness and Shannon diversity decreased and the species composition showed significant long-term shifts. Most importantly, small-sized species decreased and medium-sized species increased, which suggests that the assemblage was shaped by interspecific relationships and, perhaps, delayed effects of historical raptor persecution. A period of low population levels in the 1980s was particularly pronounced for insect-eating species, which may be related to extensive pesticide use during that period. Unexpectedly, trends in the raptor assemblage could not be attributed to landscape changes - contrasting trends were observed for species having broadly similar habitat requirements and, therefore, no general patterns could be detected for any ecological group. We conclude that, at the assemblage level, raptors are not particularly sensitive indicators of landscape change in temperate Europe.